Field of Invention
The present invention relates in general to the process of cleaning water in lakes, ponds, rivers, streams, WWTPs, food processing plants, chemical plants, mining operations, and other sites and specifically in removing phosphorus, fluoride, and arsenic impurities from water streams through a multi-stage process via the use of additives, pH control, and physical separation, resulting in a water stream with lowered concentrations of water impurities, including achievement of levels of <50 ppb phosphorus, <3 ppm fluoride, and <1 ppm arsenic.
Water commonly contains soluble ions as impurities, resulting from natural processes such as dissolution of natural minerals and materials, and from human activities including agriculture, mining, manufacturing, chemical processing, and domestic and industrial water use. Dissolved ions are potentially disruptive to the normal steady-state of ecological systems and cause effects on systems that extend beyond the water systems themselves, as well as being undesirable for human use in potable water systems.
Efficient, economical means of removal of dissolved ions are sought to provide cleaner water for the sustainment of ecological systems and prevention of human activity-induced environmental changes, eutrophication, negative toxicological effects, as well as for further clean potable water use. There is no reported economically viable full-scale process by which <50 ppb phosphorus is attainable, nor attainable in combination with removal of fluoride and arsenic and other impurities.
Description of the Prior Art
There is no prior art that uses the specific control of the pH as a specified means of control of the process and utilizes a two-stage process with potentially different complexation agents in each stage, that effectively removes phosphorus (not exclusively phosphate, but organic, oligomeric, and ortho-phosphorus, suspended and dissolved), and also removes fluoride and arsenic. There is no prior art that achieves the level of removal to <50 ppb phosphorus as does the current invention. In addition and most critically, there is no prior art that bases the reagent addition on pH targets to maximize impurity removal via the insolubility of the formed complexes.
Prior art has included lime treatment of water for impurity removal, however, never in a multistage process, See for example, Zibrida, 4,657,680 and 4,698,163. The system in the present invention is more complex and effective in impurity removal in that it carefully first dissolves and subsequently forms complexes, followed by specific pH adjustments to cause precipitation of the formed complexes. In addition, multiple stages using different reagents facilitate increased impurity removal in the present invention.
Arsenic and fluoride have previously been removed using aluminum solution, free cationic calcium, and flocculent polymer; however, at a pH of 5-8, and utilizing a membrane filter rather than a solids-liquids separation, See for example, Krulik, 6,613,230. This process and pH range will not afford the selective precipitation provided by the present invention, and the present invention provides multiple stages of complexation and tailored pH-adjustment to remove impurities based on their insolubility at the target pH levels to achieve heretofore unprecedented amounts of impurities removal.
Aluminum and flocculents were reportedly employed in a two-step removal process, however, the first step was the addition of a complexation reagent, and the second step involved a flocculation, See for example, Song, Application No. 0168325, whereas in the present invention, the stages are each comprised of the addition of reagent, pH adjustment, and a solids-liquid separation at tightly controlled pH ranges to control stoichiometry and solubility.
Use of inorganic reagents in a multi-step process along with solids/liquids separation in the prior art has precedent, See for example, Jean-Boussely, 5,759,401, however, such process differs significantly form the present invention in that it did not monitor and control pH as the key indicator or factor in maximizing the formation of complexes of additive reagents and impurities and subsequently maximizing the insolubility of these formed complexes via pH control as a means by which to remove them via solids-liquid separation.
Fluoride has been removed using inorganic reagents, however, not through the use of controlled pH adjustment to maximize the insolubility of the formed complexes as included in the present invention, See for example, Lee, 6,210,589.
There is prior art disclosing the use of lime to precipitate phosphate; however, the reported pH utilized was lower (9 to 10) than in the present invention, See for example, Bennett, 4,402,833. The present invention is based on empirical evidence that the optimal pH for insolubility of calcium complexes occurs at a pH greater than 10.2, and utilizes the higher pH in combination with flocculent to increase impurity removal. In addition, in the present invention, an additional stage, not based on lime at an alkaline pH, but rather on aluminum at a neutral pH, is used to achieve previously unprecedented levels of impurity removal.